The present invention relates generally to electronic parts. More particularly, this invention relates to an electronic part having a hook or mounting leg formed at an underside of a package to be mounted on a circuit board through using the hook or mounting leg, such as a double-molded photo-interrupter having light-emitting and light-receiving devices each molded a light transmissive synthetic resin to be packaged together into a package of an opaque synthetic resin.
Japanese Patent Laid-Open No. 6-97488, which was laid open to public on Apr. 8, 1994, discloses one example of a double-molded photo-interrupter as a background of this invention. In the photo-interrupter of this kind, an object passing between the light emitting and light receiving devices is detected depending upon the change in amount of the light received by the light receiving device.
The conventional double-molded photo-interrupter 1, shown in FIG. 1, is analogous to the technology disclosed in the above publication, and includes a light emitting device 2 and a light receiving device 3. These light emitting device 2 and light receiving device 3 are packaged together by a synthetic resin package 4. In packaging, the light emitting device 2 and the light receiving device 3 are placed opposite to each other with a predetermined spacing given. The package 4 is formed generally in a U-character form as viewed from the side. The package 4 has, at its underside, two hooks 5 formed extending downward with a spacing given between them. Each hook 5 at a tip is formed with a claw 5a. It is therefore possible to mount the photo interrupter 1 onto a top surface of a circuit board 6 by inserting the hook 5 into a through-hole 6a of the circuit board 6 and engaging the claw 5a with a backside of the circuit board 6, as shown in FIG. 2.
However, there is a problem in the FIG. 1 conventional art in that burrs 7 occur at a top surface of the hook 5 claw 5a and hook 5 side surface as shown in FIG. 2 when a resin package 4 and hence the hook 5 is formed by a metal mold. If such burrs occur on the hook 5 and the claw 5a, it becomes difficult to insert the hook 5 into a board hole 6a. Due to this, the prior art has required a post-forming process to remove away burrs 7. Moreover, such post-forming is troublesome and ultimately results in increase in photo-interrupter cost.
Therefore, it is a primary object of the present invention to provide a novel electronic part which can be mounted using a mounting leg onto a circuit board.
It is another object of the present invention to provide an electronic part free of burrs on the mounting leg which are obstructive to its mounting onto a circuit board.
It is further object of the present invention to provide a double-molding photo-interrupter fee of burrs on the mounting leg as which are obstructive to its mounting onto a circuit board.
An electronic part according to the present invention, comprises: a mounting base formed by resin molding, the mounting base being formed to have an upper surface and a lower surface, the lower surface being placed on an upper surface of a circuit board; an opening penetrating from the upper surface to the lower surface of the mounting base; and a mounting leg formed resin molding integral with the mounting base in a manner extending from the lower surface of the mounting base in a position close to the opening, the mounting leg being formed by a metal mold to form the opening.
The mounting base and the mounting leg are integrally formed through an injection mold method with a synthetic resin by a plurality of metal mold parts to define upper, lower, left and right surfaces of them. At this time, an opening is simultaneously formed by another metal mold part penetrating through the mounting base. This other metal mold part extends to a lower position than an underside of the mounting base. This other metal mold at side surfaces define side surfaces for the mounting leg. Accordingly, no burrs occur on side surfaces of the mounting leg.
In one aspect of the present invention, the mounting leg includes a claw formed at a lower end and integral with the mounting leg, the mounting leg having a side surface thereof defined by a side surface of the metal mold, and the claw having an upper surface defined by a lower surface of the metal mold. Accordingly, burrs can be prevented from being formed on the upper surface of the claw.
According to the present invention, no burrs occur on the mounting leg extending from the underside of the mounting base during resin molding. It is possible to easily insert the mounting leg into a mount hole formed in a circuit board and positively engage the claw with a board backside, differently from the prior art. Therefore, according to the present invention, there is no necessity of removing burrs in a post-forming process. It is possible to provide electronic parts of this kind at lower cost.
Incidentally, where structuring a double-molded photo-interrupter according to the present invention, the electronic part further comprising: a first portion and a second portion that are integrally formed with the mounting base, the first portion and the second portion extends upward from the upper surface of the mounting base and formed with a spacing given between; a light emitting device accommodated in the first portion, the light emitting device including a light emitting chip molded by a light transmissive resin; and a light receiving device accommodated in the second portion, the light receiving device including a light receiving chip molded by a light transmissive resin, the light receiving chip receiving light from the light emitting chip.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.